The contribution by interplanetary dust to noble gases in the atmosphere of Mars

Interplanetary dust particles accumulate significant concentrations of noble gases, implanted by the solar wind and solar energetic particles, while they are in space. When these dust particles enter the atmosphere of a planet they are heated and decelerated, depositing some of the implanted noble gases directly into the atmosphere and, if the particle survives atmospheric entry, emplacing the remainder on the surface of the planet, where it can be released by particle decomposition or by episodic surface heating. Because of the low mass of the atmosphere of Mars, compared to the atmospheres of Venus and Earth, the atmosphere of Mars is more severely influenced by the addition of noble gases by interplanetary dust. The contribution of noble gases to Mars has been modeled using estimates of the interplanetary dust flux at Mars and measurements of the noble gas contents of interplanetary dust collected from the atmosphere of the Earth. Over the past 3.6 b.y., interplanetary dust particles have contributed quantities of He-3, He-4, Ne-20 and Ne-22 comparable to the current total atmospheric inventories of these isotopes. In the present era, the rates of addition of He-3, Ne-20, Ne-22, Ar-36, and Ar-38 to the atmosphere of Mars by interplanetary dust range from about 2% to 20% of the modeled rates of addition by planetary outgassing [Pepin, 1994; Krasnopolsky and Gladstone, 1996], and the isotopic compositions of the He and Ne added by interplanetary dust are distinctly different from those assumed for planetary outgassing: He-3/He-4 (similar to)2.8x10(-4) in the interplanetary dust [Nier and Schlutter, 1992] versus almost pure 4He for outgassing of U and Th decay products, and Ne-20/Ne-22 (similar to)11.8 in the interplanetary dust [Nier, 1994] versus Ne-20/Ne-22 = 13.7 assumed for planetary outgassing in Pepin's [1994] model. Since the actual outgassing rate of Mars in the present era is not well constrained by observations, the contributions of Ne and Ar to the atmosphere of Mars by the interplanetary dust must serve, at least, as a lower limit on the current sources of these noble gases.